Building Black Holes

Black holes capture imaginations as readily as they capture light. They are enormous--the ones at the centers of galaxies are thought to be several billion times more massive than the sun. They are scary--nothing can escape the power of their gravitational pull. Even light is too slow. And they are weird--they are believed to slow down time.

But because black holes are so outlandish, it is thought that they make matter behave in ways we don't yet understand and they may therefore hold clues to the answers of some of the toughest problems in physics. If only we could see them.

Now scientists are learning to create black holes in their labs, using what are called metamaterials. These are common materials whose structures have been altered so they can make light or sound behave in bizarre ways. In 2008, Xiang Zhang at the University of California at Berkeley used metamaterials to create an invisibility cloak. Instead of reflecting light, the way most things do (which is how we see them) Zhang's materials bend light around an object, rendering it invisible.

These metamaterials can be designed so light goes in and doesn't escape, like a black hole. Of course these aren't quite the type of black holes that swallow space with their brute gravitational force. In fact, they have little or no mass at all.

"We don't have an entire sun at our disposal," laments Paul Nation, a graduate student at Dartmouth who wrote a paper in August in the journal Physical Review Letters detailing one way to make a black hole. "So we trick the light into thinking it's near a black hole."

Last year Thomas Philbin and colleagues at the University of St. Andrews in Scotland designed a system in which they were able to see what looked like the edge of a black hole, called an event horizon.

In October, two Chinese scientists, Qiang Cheng and Tie Jun Cui, at the State Key Laboratory of Millimeter Waves at Southeast University in Nanjing, China, published a paper claiming they had created a metamaterial black hole that swallowed microwaves and didn't let them out again.

Nation and his colleagues suggest building a very specific type of metamaterial black hole system designed to probe an area where the two great theories of physics, Einstein's general relativity and quantum mechanics, meet.

General relativity describes how big things like rocks and stars behave. Quantum mechanics describes how tiny things like electrons behave. Both theories stand up wonderfully to experiments; the theories are incredibly accurate. But quantum mechanics can't handle gravity, and gravity seems to break down at very small scales. This drives physicists nuts. Why should this be? The hope is that there is some explanation out there, some theory of "quantum gravity" that can help describe everything, small or big.

Black holes are the extreme case of general relativity. Matter is at its densest, gravity is at its strongest, space and time are warped in a way that light cannot behave normally. And they are, of course, mysterious. We can't see them directly, we can only infer they are there by observing how things behave near them. And the calculations that describe black holes have some real problems. Things called singularities crop up, where numbers run to infinity and make no sense. The hope is that a quantum gravity theory might iron these problems out.

Stephen Hawking showed in the 1970s that at the edges of black holes, these so called event horizons, there are some interesting quantum mechanics-related effects. The random buzz in nature spontaneously creates particles and anti-particles that immediately annihilate each other and disappear. If a pair of photons (little particles of light) appear right at a black hole's event horizon, one may fall into the black hole while the other one falls out. The photons that escape the event horizon came to be known as Hawking radiation.

"This is where quantum mechanics and general relativity begin to interact, " says Nation.

Nation described in his paper a superconducting circuit designed to mimic an event horizon in a way that will allow scientists to study Hawking radiation and maybe get some clues about quantum gravity.

"You can play quite a few games, you can custom design the pattern to get the effect you want to see and you can have states that seem totally strange to us," he says. "The idea is to test the foundational properties of quantum mechanics."

Nation proposes building a superconducting circuit made of a series of things called SQUIDS (for superconducting quantum interference devices). Each SQUID is a loop of superconducting wire that is interrupted at two places on the loop by slivers of metal that are not superconductors. When electrons, which travel in pairs when moving along a superconductor, hit the normal metal they split up and "tunnel" through the wire. This wacky electron behavior along the circuit can be made to act like an event horizon.

"This is exciting. You can do this experiment," Nation says. "No one's done it yet, but it is the long-term goal of our work and the work of many others. It's very difficult, but doable."

These little black holes may lack the drama of the supermassive ones, like the one at the center of the Milky Way that keeps our solar system in its cozy orbit. Still, If Nation and his colleagues are right, they could help us understand the even bigger picture: how everything in the universe behaves.

I'm a reporter at the Associated Press in New York, where I cover energy. I left Forbes in September, 2010 after a great 10-year run. At Forbes, I covered energy, the auto industry, and wrote a weekly science column called Out of the Labs. I started my journalism career as a...